In accordance with the International Technology Roadmap for Semiconductors (ITRS), for the 45 nm technology node 7 nm deep ultra-shallow junctions, e.g., ultra-shallow p+/n junctions, having a sheet resistance of less than 1000Ω/□ are envisaged, for example, for a transistor.
When producing ultra-shallow junctions for sub-45 nm technologies, a shallow dopant implantation is commonly used for forming shallow junction profiles. Since, when implanting dopants into a crystalline silicon substrate, specific dopants or dopant species such as boron (B), for example, may diffuse more deeply into the crystalline silicon on account of the so-called channeling effect, oftentimes the silicon is amorphized prior to the dopant implantation (so-called pre-amorphization). This may be done, for example, by means of a germanium or silicon implantation (so-called pre-amorphization implantation, PAI). By means of a PAI it may be possible, moreover, for excess silicon interstitials (Si interstitials) produced during the implantation deep in the substrate at the end of the germanium or silicon implantation profile to be spatially confined (confinement). The silicon interstitials are clearly instances of damage to the silicon crystal lattice structure in the form of silicon atoms which are situated at positions between the actual regular lattice sites of the crystal lattice, i.e., at interstices.
On account of a coarsening process, however, in the boundary region or at the interface between the amorphized partial region and the crystalline partial region of the silicon (also referred to as amorphous/crystalline silicon interface), there arise from the interstitials extended defects, also referred to as end-of-range defects or EOR defects. On account of the EOR defects, a local supersaturation of interstitials occurs, which rapidly propagates both in the direction of the substrate surface and in the direction of the silicon bulk. The resulting flow of interstitials from the EOR defect region in the direction of the substrate surface may be regarded as a cause of a transient enhanced diffusion (TED) and of the deactivation of dopants such as, for example, boron (dopant deactivation). It is widely accepted among experts here that the deactivation of the dopant atoms occurs on account of the formation of immobile dopant interstitial clusters at low temperatures.